1. Field of the Invention
This invention relates to a granular material coating apparatus, and more particularly to a granular material coating apparatus for coating on granular materials such as tablets, granules and the like used for pharmaceuticals and food products.
2. Related Art Statement
As an apparatus for applying a sugar-coating or film-coating on the surfaces of the granular materials used as articles to be coated such as the tablets, granules used for the pharmaceuticals, nuts, confectionery and the like, there have been utilized a conventional coating pan and the like in the past. However, nowadays, there are mainly used coating apparatuses of the type in which air is made to flow through an accumulated layer of the articles coated in order to facilitate drying of the coated articles.
The coating apparatus of this type includes a coating pan rotatable about a horizontal shaft and is formed therein with a multiplicate air duct holes. Coating solution and binder solution are sprayed from a spray nozzle onto the granular materials as the articles coated, which is supplied into a coating chamber of this coating pan under the rotation of the coating pan.
The type of the coating apparatus, in which the air is made to flow through the accumulated layer formed in the bottom portion of the coating chamber for drying the coated articles, is broadly divided into two categories. The first one is the category in which an exhaust duct for exhausting drying air in the coating chamber to the outside is fixed to a support base, and an opening portion of the exhaust duct is provided in opposing to the outer peripheral surface of the coating pan in sliding contact therewith. The second one is the category in which the exhaust duct extending in parallel to a rotatable shaft of the coating pan is secured to the outer peripheral surface of the coating pan.
As the coating apparatus of the first category, there is one described in the Japanese Patent Application Publication No. 51-18397 (corresponding to the U.S. Pat. No. 3,573,966), which has been sold at the market under a trade name of "Accelacoater". This coating apparatus is constructed such that there is provided a rotary drum formed in a cylindrical portion thereof with a multiplicate holes and there is disposed an exhaust device connecting to an opening portion which is in sliding contact with the outer periphery of this rotary drum in opposing to the accumulated layer of tablets. The air in the rotary drum is sucked by this exhaust device, so that the air which has flowed in from the outer periphery of the cylindrical portion of the rotary drum can flow through the accumulated layer.
A coating apparatus improved on the coating apparatus of this first category has been proposed in the Japanese Patent Laid-Open No. 63-62536. This coating apparatus has a circular frame provided at the outside of the coating pan, and the apparatus is constructed such that at least either one of an exhaust path and a gas supply path is in sliding contact with the frame, so that sealing properties can be improved and any coating pan other than that having the cylindrical shape can be used therefore.
As the coating apparatus of the second category, the one described in the Japanese Patent Application Publication No. 50-38713 (corresponding to U.S. Pat. No. 3,834,347) is the coating apparatus which has been developed firstly. In the coating pan of this coating apparatus, a plurality of exhaust ducts disposed in parallel to the rotatable shaft are secured to the outer peripheral portion of the coating pan in such a manner that the exhaust ducts cover a multiplicate holes provided in the outer peripheral portion of the coating pan. The respective exhaust ducts extend up to one end portion of the coating pan and are connected to the exhaust path through a disc valve. The drying gas is supplied into the coating pan from another end portion toward the center of rotation of the coating pan, and the drying gas, which has flowed through the accumulated material formed at the bottom of the coating pan, passes through the exhaust ducts located at the bottom and reaches the exhaust path.
In this coating apparatus, sealing is not performed on the outer periphery of the cylindrical portion of the coating pan, so that this coating apparatus has such an advantage that sealing properties can be improved. This coating apparatus is widely known under a trade name of "Hi-Coater".
As an improved type of the second category, there is one disclosed in the Japanese Patent Laid-Open No. 2-207833 (corresponding to the U.S. Pat. No. 5,050,528), which has the similar system of supplying and exhausting of the drying gas, and is known under a trade name of "Aquacoater". As a modified example of the second category, there is one described in the Japanese Patent Application Publication No. 62-19135 (corresponding to the International Application No. PCT/EP84/00072). In this coating apparatus, both of the gas supplying and the exhausting are performed through ducts, and the respective ducts, a gas supply path and an exhaust path are successively connected to or shut off by a distributor provided at an end of the coating pan.
In the above-described coating apparatus, there is a way of use where the drying gas is made to flow from the inside to the outside through the accumulated layer. On the contrary, there is another way of use where the drying gas is made to flow from the outside to the inside through the accumulated layer. Selection of either one of the flowing direction as described above depends on various conditions including the types of the articles to be coated, the progressional stage of process and the like. Accordingly, it is desirable that changeover of the direction of the drying gas can be easily made.
Furthermore, there is such a case that, after coating is finished to make tablets of one type, another type of coating is performed in the same coating apparatus. In that case, it is desirable of cleaning the coating pan perfectly in the viewpoints of GMP (Good Manufacturing Practice) and the validation for manufacturing the high quality products.
However, in the coating apparatus of the first category, which is described in the Japanese Patent Laid-Open No. 63-62536 as above, it is necessary to change over a gas supply duct connecting to a blower into either lower duct or upper duct, otherwise to provide a blast changeover device to be connected to a gas supply path and an exhaust path. In the apparatus, it is necessary to provide an additional mechanism for changing over a direction of the flow of the drying air to an opposite direction thereto, so that the installation area becomes disadvantageously larger.
Furthermore, in the coating apparatus of the second category, a plurality of ducts are secured to the outer side of the coating pan in the axial direction, whereby not only resistance for ventilation of the drying gas has been increased, but also the cleaning works for the coating pan, also for the ducts, have been disadvantageously difficult. In order to manufacture the high quality products, it is inevitable to perform the full cleaning works for the above-described parts, and there has been the difficulties of the cleaning works as the serious problem from the viewpoint of GMP and the validation.